Robots are widely used in industry for tasks such as welding and painting. In such tasks, the robot gripper is attached to a tool, and the robot is controlled to apply the tool to, or manipulate the tool near a stationary workpiece. The task of causing the robot tool point to intersect an identified point (such as a corner or the centroid) on an object is known as "targeting". A more complex task which may be performed by robots is to acquire parts on a moving conveyor belt. Such tasks may be found in industry for inspection and sorting, and in mail carrier applications for singulation of unsingulated mailpieces. Upon completion of "targeting", the robot may pick up the object with a gripper such as a vacuum cup or "sticky tape", or it may apply a dot of paint or ink to the surface of the object to identify parts in an automated inspection system.
If static and dynamic information and equations characterizing the robot's motion were available from the manufacturer, a user could generate software for identifying the location of the target and for directing the various motors and controls in such a fashion as to cause the robot to acquire the target. However, such information is ordinarily not available from the robot manufacturer.
Commercial software is available which provides the capability of interfacing specific robots and vision systems with linear belt conveyors. One example of such a software package is "Conveyor Tracking (moving line)", manufactured by Adept, whose address is 1212 Bordeaux Drive, Sunnyvale, Calif. 94089. This software package is included with their V+ language and is adapted to couple an Adept robot to a linear conveyor provided with a speed indicator, and optionally to a vision system. Operation of such software commonly causes the gripper velocity to be matched to that of the conveyor, physically tracking the item to be grasped (the "target") with the gripper (or other tool) at a location above the target. When tracking is achieved, the gripper or tool is lowered, still tracking the target. The robot then gasps and removes the part or performs a tool function, as appropriate.
Such commercial software provides the desired function, but is specific to a particular robot and vision system, and limited to linear conveyors. In general, such commercial software tends to be robot and conveyor specific, and the quantities of the software packages which are sold tends to be small, and therefore the cost of software generation must be spread over only few units, so the unit cost tends to be high. The cycle time for acquisition tends to be higher than desirable because of the need for tracking of the workpiece before acquisition. Improved robot control is desired.